Question

The heat of reaction for $C_{10}{H}_8\left(s\right)+12O_2\left(g\right)\to 10C{O}_2\left(g\right)+4H_{2}O\left(l\right)$ at constant volume is (1229.892 Kcal at ${25}^0$C. Calculate the heat of reaction at constant pressure at ${25}^0$C.

• A. 1992.367 Kcal
• B. 1231.084 Kcal
• C. 5671.315 Kcal
• D. 2234.567 Kcal

Answer 1

Answer: (B)

1231.084 Kcal

Solution:-

Given reaction:-

${C_{10}{H}_8}_{\left(s\right)}+12{O_2}_{\left(g\right)}⟶10{C{O}_2}_{\left(g\right)}+4{H_{2}O}_{\left(l\right)}$

$\Delta n_g=n_P-n_R=10-12=-2$

Given:-

$\Delta E=-1229.892kcal(\because \text{combustion is always exothermic})$

$T=25℃=(25+273)=298K$

Now as we know that,

$\Delta H=\Delta E+\Delta n_{g}RT$

$\Rightarrow \Delta H=1229.892+(-2\times 2\times {10}^{-3}\times 298)$

$\Rightarrow \Delta H=-1229.892-1.192=-1231.084kcal$

Hence the heat of given reaction of given reaction at $25℃$ is $-1231.084kcal$.